Worms/ˈwɜːrm/ are many different distantly related animals that typically have a long cylindrical tube-like body and no limbs. Worms vary in size from microscopic to over 1 metre (3.3 ft) in length for marine polychaete worms (bristle worms),[1] 6.7 metres (22 ft) for the African giant earthworm, Microchaetus,[2] and 58 metres (190 ft) for the marine nemertean worm (bootlace worm), Lineus longissimus.[3] Various types of worm occupy a small variety of parasitic niches, living inside the bodies of other animals. Free-living worm species do not live on land, but instead live in marine or freshwater environments, or underground by burrowing.

Contents

In everyday language, the term worm is also applied to various other living forms such as larvae, insects, millipedes, centipedes, shipworms (teredo worms), or even some vertebrates (creatures with a backbone) such as blindworms and caecilians. Worms can be divided into several groups, but are still technically decomposers.

The second group contains the threadworms, roundworms, and hookworms. This phylum is called Nematoda. Threadworms may be microscopic, such as the vinegar eelworm, or more than 1 metre (3 feet) long. They are found in damp earth, moss, decaying substances, fresh water, or salt water. Some roundworms are also parasites. The Guinea worm, for example, gets under the skin of the feet and legs of people living in tropical countries.

The third group consists of the segmented worms, with bodies divided into segments, or rings. This phylum is called Annelida. Among these are the earthworms and the bristle worms of the sea.

In earlier taxonomic classification, all the above were included in the now obsolete group Vermes, a paraphyletic assemblage of unrelated phyla.